Several processes and devices used in connection therewith require a prescribed constant temperature of thermal energy of the heat exchange media used to operate same if it is to perform within a coefficient of performance (C.O.P.) or top efficiency of operation to which it is designed. Examples of such are absorption refrigeration machines, space heating systems, Rankin cycle engines, Sterling cycle engines, sterilization processes, pasturizing processes, and food processing, to name a few. It is desirable to utilize solar radiant energy as a source of the thermal energy for operating such devices and processes.
To date, solar energy systems employ a working media--usually liquid--which is pumped through the solar energy collector apparatus and therein the working media is heated by the exchange of absorbed solar energy within the collector. The liquid after receiving the thermal energy in the solar collector apparatus is placed in a storage tank for use by the demand of the process or device in the system. The liquid media is withdrawn usually from the hotter top strata of the tank and circulated through the heat operated device wherein heat is exchanged from the circulated media to run the device, and then the media at lower temperature is returned to the lower cooler strata of the storage tank. Liquid from the lower strata therein is transferred again to the collectors for raising its temperature and the cycle is repeated. The storage tank is utilized in such manner under what is known as stratified storage of the liquid. Stratified storage tanks are subject to some circulation within them by convection and by the liquid movement into and out of the tank. See for example U.S. Pat. No. 4,034,912 utilizing a stratified storage tank and control for putting the stored energy in the system switched between solar heating apparatus and conventional heating apparatus to meet the system thermal requirements. Some of the prior systems using stratified tanks have incorporated structural baffles to separate the hotter and colder liquid strata therein. Examples of this are set forth in U.S. Pat. Nos. 3,996,759; 4,027,821; and 4,037,785.
Moreover, the movement of the liquid working media into and through the solar energy collector apparatus is presently regulated on a control cycle as a function of plural variables, namely, quantity, time, and flow rate. However, the solar energy collector is subject to variable output because of weather factors, such as cloud cover or haze, and angular incidents and quantity of the radiation on the collector will vary during the day and seasonally. This presents a serious control problem for maintaining a desired constant temperature media available for the heat utilization device or process.